The U.S. Nuclear Regulatory Commission (NRC) sent a letter to Exelon Corp. (NYSE: EXC) to address the NRC’s concerns with the 1,700 MW Dresden Nuclear Station’s response plan for external flooding events. The two-unit plant is located in Morris, Ill.
NRC inspectors identified multiple areas of concern during recent inspections conducted in response to the disaster at the Fukushima Daiichi nuclear power plant in Japan. The issues pertain to the plant’s plan to respond to a Probable Maximum Flood, which is a hypothetical flooding level that represents the largest conceivable flood from a combination of the most severe meteorological and hydrologic conditions. Such conditions are highly improbably and have never been known to happen in the area. The issues with the flood plan do not represent an immediate safety issue but are an area where NRC would like additional information.
The two main areas of concerns with the flood response plan are: The quality and viability of the procedure, and the availability and capability of equipment specified in the response plan to fulfill their intended functions.
Dresden was originally licensed for operation in 1966 for a flood value of 506.4 feet above mean sea level. The reactor and other plant structures were constructed at 517 feet above mean sea level, 10 feet above historic flood levels. The NRC changed flood design criteria in 1982, and Dresden developed a response plan to address the disparity between the original and the revised design bases for flooding.
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